1. Field of the Invention
This invention relates to a recording head for a perpendicular magnetization medium having a single layer magnetic film.
2. Description of the Related Art
In recent years, as reduction in size and increase in capacity of a magnetic disk drive proceeds, refinement of magnetic particles in a medium is demanded. However, in a conventional recording system called an in-plane recording system, remarkable refinement of magnetic particles is difficult because it results a factor of thermal instability. Therefore, a perpendicular magnetization recording system which is superior in thermo-magnetic relaxation and so forth is examined. In an ordinary perpendicular magnetic recording system, a two-layer film medium wherein a soft magnetic ground layer is layered on a substrate and a perpendicular magnetization film is layered on the soft magnetic ground layer is used.
However, since reduction of magnetic noise is difficult with a two-layer film medium, another perpendicular magnetic recording system which employs a single layer magnetic film medium wherein a perpendicular magnetization film is layered or laminated on a substrate directly or with an insulation film interposed therebetween has been investigated recently. However, where a single layer perpendicular magnetization film which does not have a soft magnetic ground layer on a substrate is used as a recording medium, it is essentially required to develop a recording head (writing head) having a steep magnetic field gradient.
In a conventional perpendicular recording system which employs a single layer magnetic film medium, an ordinary ring head for the in-plane recording system, that is, a metal-in-gap (MIG) ring head or a thin film ring head whose leading pole and trailing pole have an equal height as viewed from the plane of the medium, is used. A general structure of a conventional thin film ring head will now be described with reference to FIGS. 1 and 2. A conventional head slider 2 has a pair of floating rails 4 and 6, and a thin film ring head 8 is formed at a downstream side end portion 2a of the head slider 2 at which the floating rail 4 is located in a direction of movement of a magnetic disk medium indicated by an arrow mark P.
Referring to FIG. 2, an enlarged sectional view of the thin film ring head 8 is shown together with a single layer magnetic film medium 10. The single layer magnetic film medium 10 includes a non-magnetic substrate 12, and a perpendicular magnetization film 14 made of, for example, Co-Cr and layered on the non-magnetic substrate 12. A non-magnetic substrate 16 of the thin film ring head 8 forms part of the head slider 2 and is formed from, for example, Al.sub.2 O.sub.3 TiC. A leading pole 18 formed from a magnetic thin film of a permalloy (Ni-Fe) or a like material is formed on the non-magnetic substrate 16.
Reference 20 denotes a trailing pole formed similarly from a magnetic thin film of a permalloy or a like material, and a small gap 22 is defined between an end 18a of the leading pole 18 and an end 20a of the trailing pole 20 which oppose to the medium 10. A rear end portion 18b of the leading pole 18 and a rear end portion 20b of the trailing pole 20 are held in contact with each other over a predetermined length, and generally a ring structure is defined by the trailing pole 20 and the leading pole 18. The length of the small gap 22 is approximately 0.5 .mu.m.
A spiral thin film coil 24 made of copper (Cu) is provided around the contacting portions of the leading pole 18 and the trailing pole 20. The leading pole 18, trailing pole 20 and thin film coil 24 are embedded in a insulation layer 26. FIG. 3 shows an enlarged view of a portion in the proximity of the end portion of the conventional ring head 8. In the perpendicular magnetic recording system, the axis of easy magnetization of the medium is in a direction perpendicular to the plane of the medium film, and consequently, a magnetic field component in a perpendicular direction of a magnetic vector (head magnetic field) produced in the medium by the magnetic head is used to write data onto the recording medium.
The perpendicular magnetic field component Hz of the conventional ring head 8 has a point symmetrical distribution centered at the small gap 22 as seen in FIG. 4 and has two peaks of the different signs in the proximity of an edge of the leading pole 18 facing the small gap 22 and in the proximity of an edge of the trailing pole 20 facing the small gap 22. Therefore, although the medium is magnetized (recorded) once by the peak magnetic field on the leading pole 18 side, it is re-written substantially completely by the peak magnetic field on the trailing pole 20 side.
Accordingly, magnetization transition is formed by a magnetic field gradient at a portion A adjacent the trailing side (on the side from which the medium goes away) with respect to the peak magnetic field which appears in the proximity of the edge of the trailing pole 20 which faces the small gap 22. However, since the magnetic field gradient at this portion is very moderate, it is difficult to form a steep magnetization transition. In order to compensate for this drawback, the medium is required to have a very strong perpendicular magnetization orientation property and magnetic anisotropy.
FIG. 5 illustrates a relationship between magnetic fluxes 28 of the conventional ring head 8 and the single layer magnetic film medium 10 having the perpendicular magnetization film 14 of a single layer. Almost all of the magnetic fluxes 28 emerging from the end 18a of the leading pole 18 pass through the perpendicular magnetization film 14 and return to the trailing pole 20. Since the perpendicular magnetization film 14 layered on the substrate 12 is less than 0.1 .mu.m in thickness and is very thin, in order to generate a large magnetic field component in a perpendicular direction in the perpendicular magnetization film 14, it is essentially required to use the ring head 8 whose gap length G1 is set to a very small length. The gap length G1 is, for example, approximately 0.5 .mu.m.
For comparison, a relationship between a conventional magnetic recording head 37 and a two-layer magnetic film perpendicular magnetization medium 30 is illustrated in FIG. 6. The two-layer magnetic film perpendicular magnetization medium 30 includes a non-magnetic substrate 32, a soft magnetic ground film 34 of Ni-Fe or a like material layered on the non-magnetic substrate 32 and a perpendicular magnetization layer 36 made of Co-Cr and layered on the soft magnetic ground film 34. The soft magnetic ground film 34 has a thickness of more than 1 .mu.m, and the perpendicular magnetization layer 36 has a thickness of less than 0.1 .mu.m. Almost all of magnetic fluxes 42 emerging from an end 38a of a main magnetic pole 38 of the magnetic recording head 37 pass through the soft magnetic ground film 34 and return to an auxiliary magnetic pole 40.
In the two-layer magnetic film perpendicular magnetization medium 30, since almost all of the magnetic fluxes 42 pass through the soft magnetic ground film 34 of a large film thickness and return to the auxiliary magnetic pole 40 in this manner, it is easy to apply a steep magnetic field in a perpendicular direction to the perpendicular magnetization layer 36. Consequently, the gap length G2 defined between the end 38a of the main magnetic pole 38 and an end 40a of the auxiliary magnetic pole 40 need not be set to a small length as in the thin film ring head 8 shown in FIG. 5, and the gap length G2 is usually set to a large length of approximately 10 .mu.m.
As apparent from comparison between FIGS. 5 and 6, the ring head 8 whose gap length G1 is very small must be used for the single layer magnetic film medium 10, for the two-layer magnetic film perpendicular magnetization medium 30, the magnetic recording head 37 which has a construction quite different from that of the thin film ring head 8 and has a very large gap length G2 is used. For a recording head for a two-layer magnetic film perpendicular magnetization medium, several recording heads which are constructed such that an auxiliary magnetic pole is spaced from a surface of a medium farther than a main magnetic pole have been proposed (Japanese Patent Laid-Open Application No. Heisei 1-151011 and Japanese Patent Laid-Open Application No. Heisei 4-90101).
However, for the conventional ring head 8 for the single layer magnetic film medium 10, a ring head wherein the distance from the end 18a of the leading pole 18 to the surface of the medium and the distance from the end 20a of the trailing pole 20 to the surface of the medium are equal to each other is used. Where the thin film ring head 8 of such a construction just described is used as a recording head for a single layer magnetic film perpendicular magnetization medium, since a very strong perpendicular magnetic orientation property and perpendicular magnetic anisotropy are required for the medium, it is not easy to manufacture the medium. Where a medium having insufficient magnetic characteristics is used, the recording and/or reproduction characteristic is deteriorated remarkably.